The present invention relates to petrochemistry, specifically to a method for the extraction of mercaptans from petroleum and gas condensates, and may find application in the petroleum, natural gas, petroleum-processing and petrochemical industry.
Known methods for the extraction of mercaptan from oil and gas condensates involve their treatment with an 18 to 25% aqueous solution of an alkali metal hydroxide, ethyl alcohol, ketone and formaldehyde, with the subsequent release of the purified product (see Russian Author's Certificates Nos. 1567598 and 1579927 issued in 1990).
Another known method for the extraction of mercaptan from gas condensates is by a process which involves treatment with a sodium salt of arylsulfinic acid with the subsequent release of the purified product (see Russian Author's Certificate No. 1810377 issued in 1993.)
The principal drawbacks of the known methods consist in the great amount of scarce and costly reagents which must be consumed in the process (namely, ketones, aldehydes, sulfinic acids), since during the extraction of the mercaptan from the raw material, the cited reagents which are applied enter into a permanent, irreversible reaction with the mercaptan, resulting in the formation of unregenerable organic compounds containing oxygen and sulfur.
A method is also known for the extraction of mercaptan from petroleum and petroleum byproducts by means of processing the raw material with a cuprate of the naphthene in the oil with the weight ratio of the copper salt to the mercaptan in the raw material falling within the range of from 3 to 4:1 (see Russian Author's Certificate No. 1616959 issued in 1990.)
The principal disadvantages of the aforesaid method are: the high rate of consumption of the scarce reagent involved, especially when purifying petroleum with a high content of sour sulfur (mercaptan sulfur), the difficulty of separating the resulting precipitate from the purified product, the formation of a waste byproduct (a precipitate) which is difficult to utilize, as well as the loss of the purified product together with the discarded residue.
The method which most closely resembles the method of the present invention both in its technological essence and the obtained result is a method for the extraction of mercaptans from petroleum distillates by processing with the oxygen of the air in an aqueous solution of an alkali metal hydroxide, in the presence of a cobalt octocarboxytetraphenylphthalocyanine catalyst, in an amount of 0.005 to 0.2 weight percent, as calculated with respect to the aqueous solution of the alkali metal hydroxide (see Russian Author's Certificate No. 1824421 issued in 1991). The principal disadvantages of this method are to be found in the insufficiently high degree of mercaptan extraction from the raw material as well as the low stability of the catalytic activity of the catalyst.
It is an object of the present invention to increase the degree to which the raw material is purified and the mercaptan extracted, to increase the stability of the catalytic activity of the catalyst under the conditions of the purification of petroleum and gas condensate.